The present invention relates to hydrolic shock absorbers, and in particular to a telescoping piston and metering design therefor, as well as a related method.
Virtually all manufacturing processes involve movement of some kind. In production machinery, this movement can involve linear transfers, rotary index motions, fast feeds, etc. At some point, these motions change direction or come to a complete stop. Any moving object possesses kinetic energy as a result of its motion. When the object changes direction or is brought to rest, the dissipation of this kinetic energy can result in destructive shock forces with the structural and operating parts of the machine. Kinetic energy increases as an exponential function of velocity. The heavier the object, or the faster it travels, the more kinetic energy it possesses. An increase in production rates is only possible by dissipating this kinetic energy smoothly and thereby eliminating destructive deceleration forces.
Older methods of energy absorption, such as rubber buffers, springs, hydraulic dash pots and cylinder cushions, do not provide the smooth deceleration characteristics required for most modern machinery. Such prior art devices are generally nonlinear, and produce high peak forces at some point during their stroke.
Industrial shock absorbers have been developed to meet at least some of these needs. Currently, there are two basic kinds of linear decelerating shock absorbers, namely, adjustable and nonadjustable. Adjustable shock absorbers, such as that disclosed in U.S. Pat. No. 4,122,923, are adapted for use in conjunction with a wide range of loads or weights. For instance, a single adjustable shock absorber, when properly adjusted, can decelerate loads from 24 pounds to 2,400 pounds, which is a ratio of 100 to 1. However, once adjusted, such devices function as a nonadjustable shock absorber, which is limited to a weight range or ratio of 2 to 1, as for example 24 pounds to 48 pounds. The advantage of an adjustable shock absorber is that it can be adjusted to any one of the weights from 24 pounds to 2,400 pounds. However, a disadvantage of an adjustable shock absorber is that, once it is adjusted for one weight, it cannot accommodate substantial variation in weight, propelling force, environmental conditions, or other similar factors.
Nonadjustable shock absorbers, such as those disclosed in U.S. Pat. No. 5,682,967, cannot be used for a wide variety of different applications, but rather are custom designed to accommodate a specific application. Nonadjustable shock absorbers are capable of accommodating a range of weights with ratios as high as 10 to 1. A nonadjustable shock absorber can also be designed to provide a customer specific deceleration or reaction force, which produces better audible and visual performance to the human observer. Some types of nonadjustable shock absorbers have a piston tube with a special orifice pattern or profile to create a self-compensating feature which neutralizes the effect of changing fluid coefficients, weight velocity, temperature and fluid compressibility, and is therefore beneficial in many applications. Even though a nonadjustable shock absorber can be designed to accommodate a range of weights, it cannot accommodate a weight range nearly as wide as an adjustable shock absorber.
One drawback associated with current shock absorbers is that both adjustable and nonadjustable shock absorber designs are rather complex, and relatively difficult to manufacture. For example, the nonadjustable shock absorber disclosed in U.S. Pat. No. 5,682,967 utilizes a series of precisely formed, discrete circular metering orifices spaced at predetermined points along the length of an inner piston tube to achieve relatively constant linear deceleration. While such constructions are generally effective, the precision machining required to ensure the inner piston tube and related circular orifices are positioned at the correct positions, and are of the appropriate diameters, is an expensive and time-consuming task. Adjustable shock absorbers, such as that disclosed in U.S. Pat. No. 4,122,923, typically included complicated valving arrangements, which are also expensive to manufacture and assemble.
Furthermore, current industrial shock absorbers incorporate a plurality of individual parts which must be properly assembled to make the designed shock absorber. These individual parts are custom designed for a particular application, thereby increasing fabrication, inventory and other manufacturing costs.
Hence, the need exists for an industrial shock absorber having a relatively uncomplicated design, so as to reduce manufacturing costs and improve reliability. Also, it would be beneficial to have an uncomplicated hydraulic shock absorber design that is highly effective in decelerating loads with the lowest possible force in the shortest possible time, thereby eliminating damaging force peaks and shock damage to machines and equipment. It would also be beneficial to have a shock absorber design that possesses the benefits of a nonadjustable shock absorber, yet can be used for a wide range of loads or weights, such as those ranges typically associated with adjustable shock absorbers.